2 research outputs found
Geons with spin and charge
We construct new geon-type black holes in D>3 dimensions for Einstein's
theory coupled to gauge fields. A static nondegenerate vacuum black hole has a
geon quotient provided the spatial section admits a suitable discrete isometry,
and an antisymmetric tensor field of rank 2 or D-2 with a pure F^2 action can
be included by an appropriate (and in most cases nontrivial) choice of the
field strength bundle. We find rotating geons as quotients of the
Myers-Perry(-AdS) solution when D is odd and not equal to 7. For other D we
show that such rotating geons, if they exist at all, cannot be continuously
deformed to zero angular momentum. With a negative cosmological constant, we
construct geons with angular momenta on a torus at the infinity. As an example
of a nonabelian gauge field, we show that the D=4 spherically symmetric SU(2)
black hole admits a geon version with a trivial gauge bundle. Various
generalisations, including both black-brane geons and Yang-Mills theories with
Chern-Simons terms, are briefly discussed.Comment: 26 pages, 1 figure. LaTeX with amssymb, amsmath. (v2: References and
a figure added.
On Physical Equivalence between Nonlinear Gravity Theories
We argue that in a nonlinear gravity theory, which according to well-known
results is dynamically equivalent to a self-gravitating scalar field in General
Relativity, the true physical variables are exactly those which describe the
equivalent general-relativistic model (these variables are known as Einstein
frame). Whenever such variables cannot be defined, there are strong indications
that the original theory is unphysical. We explicitly show how to map, in the
presence of matter, the Jordan frame to the Einstein one and backwards. We
study energetics for asymptotically flat solutions. This is based on the
second-order dynamics obtained, without changing the metric, by the use of a
Helmholtz Lagrangian. We prove for a large class of these Lagrangians that the
ADM energy is positive for solutions close to flat space. The proof of this
Positive Energy Theorem relies on the existence of the Einstein frame, since in
the (Helmholtz--)Jordan frame the Dominant Energy Condition does not hold and
the field variables are unrelated to the total energy of the system.Comment: 37 pp., TO-JLL-P 3/93 Dec 199